This invention is generally directed to improved cold pressure fixable toner compositions, and more specifically the present invention is directed to magnetic single component development, pressure fixable, encapsulated toners containing, for example, a core component inclusive of magnetite and thereover a durable polymeric shell prepared by interfacial polymerization. In one embodiment there is provided in accordance with the present invention an improved encapsulated cold pressure fixable toner composition wherein the shell is comprised of the reaction product of a first isocyanate component selected, for example, from the group consisting of polymethylene polyphenyl isocyanates (PAPI) and diphenylmethane diisocyanates (Isonate), and a second amine component as illustrated in more detail hereinafter. In another embodiment of the present invention, the toner compositions obtained include thereon an electroconductive material thereby enabling compositions with a controlled, and stable resistivity such as, for example, from about 1.times.10.sup.3 to about 1.times.10.sup.8, and preferably from about 5.times.10.sup.4 and 1.times.10.sup.7 ohm-cm, which toners are particularly useful for inductive development processes. The aforementioned toner composition possesses a number of advantages including the ability to provide a substantially higher final image fix to plain paper in some instances; a shell with substantially improved mechanical properties; and moreover, the shell monomers selected possess low vapor pressures, thus reducing environment hazards, which is not the situation with some of the prior art toner shells. Moreover, the shell capsules employed in the prior art often do not withstand shear forces or impact during use as toners, a disadvantage alleviated with the encapsulated toner compositions of the present invention. Thus, for example, with the toner compositions of the present invention, the shell does not rupture prematurely causing the adhesive core component comprised, for example, of a polymer and magnetite to become exposed, which upon contact with other toner particles or ionographic subsystem component surfaces forms undesirable agglomerates. The toner compositions of the present invention are useful for permitting the development of images in electrophotographic imaging systems including electrostatic imaging systems with electroreceptor wherein pressure fixing, especially fixing in the absence of heat is selected.
Cold pressure fixing processes are known. These processes have a number of advantages in comparison to heat fixing, primarily relating to the requirements for less energy, since the toner compositions used can be fused at room temperature. Nevertheless, many of the prior art cold pressure fixable toner compositions, particularly those prepared by conventional melt blending processes, suffer from a number of deficiencies. For example, these toner compositions must usually be fused under very high pressures to achieve acceptable image fix to plain paper. Also, with some of the prior art processes, substantial image spreading can result from the high pressures required. Additionally, the cold pressure fixing toner compositions of the prior art have other disadvantges in that, for example, these compositions when used for development cause in some instances images with high gloss that are of low crease resistance. Furthermore, the use of high fixing pressures results in images with a waxy feel, and crushed paper fibers referred to as paper calendering. In contrast, images developed with the cold pressure compositions of the present invention possess a low gloss appearance on plain paper, and furthermore, these images in most instances possess a substantially improved image fix level at relatively low fixing pressures with significantly improved resistance to removal or flaking when creased. Also, the toner compositions prepared in accordance with the process of the present invention have durable shells thus enabling images with substantially no background deposits. Also, with the toner compositions of the present invention, particularly with respect to their selection for single component inductive development processes, the toner particles contain a complete uniform and substantially permanently attached electroconductive material thereby imparting stable electroconductive surface charge to the particles inclusive of situations wherein these particles are subjected to vigorous agitation, a disadvantage associated with many prior art toner compositions wherein, for example, electroconductive dry surface additives such as carbon black are selected. Further, with the aforementioned prior art toner compositions there is usually obtained images of low quality with substantial background deposits, particularly after a number of imaging cycles especially subsequent to vigorous mechanical agitation which causes toner electroconductivity instability most likely since the additives such as carbon black are not permanently retained on the surface of the toner particles.
There are disclosed in U.S. Pat. No. 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, which shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. In the '169 patent, it is indicated that when magnetite or carbon black is selected they must be treated in a separate process to prevent migration thereof to the oil phase.
Interfacial polymerization processes are described in British Patent Publication No. 1,371,179, the disclosure of which is totally incorporated herein by reference, which publication illustrates a method of microencapsulation based on in situ interfacial condensation polymerization. More specifically, this publication discloses a process which permits the encapsulation of organic pesticides by the hydrolysis of polymethylene polyphenylisocyanate, or toluene diisocyanate monomers. Also, the wall forming reaction disclosed in the aforementioned publication is initiated by heating the mixture to an elevated temperature at which point the isocyanate monomers are hydrolyzed at the interface to form amines, which in turn react with unhydrolyzed isocyanate monomers to enable the formation of a polyurea microcapsule wall.
Moreover, there is disclosed in U.S. Pat. No. 4,407,922, the disclosure of which is totally incorporated herein by reference, interfacial polymerization processes for pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctadecylvinylether-co-maleic anhydride as a soft component.
Additionally, illustrated in a copending application U.S. Ser. No. 621,307, entitled Single Component Cold Pressure Fixable Encapsulated Toner Composition, the disclosure of which is totally incorporated herein by reference, are single component development cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. A similar teaching is present in copending application U.S. Ser. No. 718,676, the disclosure of which is totally incorporated herein by reference, directed to single component magnetic cold pressure fixable toner compositions. In the aforementioned application, the core can be comprised of magnetite and a polyisobutylene of a specific molecular weight encapsulated in a polymeric shell material generated by an interfacial polymerization process. More specifically, there are illustrated in the aforementioned copending application cold pressure fixable magnetic single component developers with carbon black and large amounts of magnetite.
Furthermore, other prior art, primarily of background interest, includes U.S. Pat. Nos. 4,254,201; 4,465,755; and Japanese Patent Publication No. 58-100857. The Japanese publication discloses a capsule toner with high mechanical strength, which is comprised of a core material including a display recording material, a binder, and an outer shell, which outer shell is preferably comprised of a polyurea resin. In the '091 patent, there are disclosed encapsulated electrostatographic toners wherein the shell material comprises at least one resin selected from polyurethane resins, a polyurea resin, or a polyamide resin. In addition, the '755 patent discloses a pressure fixable toner comprising encapsulated particles containing a curing agent, and wherein the shell is comprised of a polyurethane, a polyurea, or a polythiourethane. Moreover, in the '201 patent there are illustrated pressure sensitive adhesive toners comprised of clustered encapsulated porous particles, which toners are prepared by spray drying an aqueous dispersion of the granules containing an encapsulated material.
Furthermore, there are illustrated in U.S. Pat. No. 4,280,833 encapsulated materials prepared by interfacial polymerization in aqueous herbicidal compositions containing these capsules. More specifically, as indicated in column 4, beginning at line 9, there is disclosed a process for encapsulating the water immiscible material within the shell of the polyurea, a water immiscible organic phase which consists of a water immiscible material, that is the material to be encapsulated, and polymethyl polyphenyl isocyanate is added to the aqueous phase with agitation to form a dispersion of small droplets of the water immiscible phase within the aqueous phase; and thereafter, a polyfunctional amine is added with continuous agitation to the organic aqueous dispersion, reference column 4, lines 15 to 27. Also, of interest is the disclosure in column 5, line 50, wherein the amine selected can be diethylene triamine, and the core material can be any liquid, oil, meltable solid or solvent soluble material, reference column 4, line 30. A similar teaching is present in U.S. Pat. No. 4,417,916.
In U.S. Pat. No. 4,599,271 there are illustrated microcapsules obtained by mixing organic materials in water emulsions at reaction parameters that permit the emulsified organic droplets of each emulsion to collide with one another, reference the disclosure in column 4, lines 5 to 35. Examples of polymeric shells are illustrated, for example, in column 5, beginning at line 40, and include isocyanate compounds such as toluene diisocyanate, and polymethylene polyphenyl isocyanates. Further, in column 6, at line 54, it is indicated that the microcapsules disclosed are not limited to use on carbonless copying systems; rather, the film material could comprise other components including xerographic toners, see column 6, line 54.
Other prior art of interest includes U.S. Pat. No. 4,520,091, which illustrates an encapsulated toner material wherein the shell can be formed by reacting a compound having an isocyanate with a polyamide; reference column 4, lines 30 to 61, and column 5, line 19; and U.S. Pat. No. 3,900,669 illustrating a pressure sensitive recording sheet comprising a microcapsule with polyurea walls, and wherein polymethylene polyphenyl isocyanate can be reacted with a polyamide to produce the shell, see column 4, line 34.
Additionally, in U.S. Pat. No. 4,476,211 there is disclosed a process for the preparation of toner compositions which can be selected for cold pressure fixing processes, which compositions are provided with a colored electroconductive powder on the outer surface thereof, such powders including, for example, carbon black and colloidal graphite, which are spray dried together with the wet toner dispersion. Also, U.S. Pat. No. 3,196,032 and Dutch Patent Application No. 7203523 illustrate a process of rendering single component developer powders electroconductive by the deposition of fine carbon particles on the toner surfaces. Disadvantages associated with the aforementioned toners include the release of the carbon black particles from the surface resulting in a loss of conductivity stability, and also resulting in contamination and premature failure of the electrical systems of the electrophotographic imaging apparatus within which they are incorporated. Moreover, British Pat. No. 940,577 and U.S. Pat. No. 4,286,037 illustrate the use of water soluble and water insoluble antistatic agents as electroconductive coating materials, however, high impractical loadings such as, for example, 8 to 35 percent by weight of ammonium salts are needed to obtain a resistivity of 10.sup.7 to 10.sup.11 ohm-cm, which adversely effects the particle size; flow and fusing properties of the toner particles, and has other disadvantages.
Although many of the aforementioned encapsulated toners are suitable for their intended purposes, there remains a need for single component development cold pressure fixable toner compositions that exhibit significantly improved image fix and crease resistance properties when applied to plain paper and fixed at relatively low fixing pressures. Additionally, there is a need for single component encapsulated toner compositions with durable shells that do not rupture prematurely resulting in undesirable toner agglomerations. There is also a need for single component encapsulated toner compositions that are of lower cost in comparison to similar prior art toner compositions. There is also a need for single component development encapsulated toner compositions which exhibit stable conductivity when subjected to agitation in developer subsystems.